SECTIONAL TRANSACTIONS— D. 441 



application of the principle of adaptive radiation and convergence. (4) The 

 general habits, the resting attitudes, and the special protective and aggressive 

 reactions of animals are closely correlated with their scheme of coloration, 

 and their surroundings, and are to be explained in terms of the psychology 

 of vision. 



Mr. D. Lack. — Bird courtship and aggressive behaviour (ii.o). 



The term ' courtship display ' has been applied extremely loosely in bird 

 behaviour. Many displays really serve a threat function, and displays which 

 are directed at the female may occur in three different phases of the breeding 

 cycle : (i) by the unmated male before pairing up ; (2) by one or both sexes 

 after the pair have associated and leading up to copulation ; (3) by both sexes 

 during the post-nuptial period. 



Sexual selection in Darwin's sense typically has reference only to the 

 first phase. The evidence for preferential matings in birds is summarised. 



Recent experiments with stuffed specimens illustrate the influence of 

 threat and display characters in producing aggressive behaviour and court- 

 ship, and the part they play in sex recognition. Experiments with robins, 

 which will sometimes attack parts of stuffed specimens, show that the 

 problem is not simply one of ' recognition,' but is very complex. 



Mr. L H. BuRKiLL. — Insect vision and the perception of flowers (11.30). 



That bees and butterflies see the flowers they visit is axiomatic. A feeding 

 hive-bee by differential stimuli in the upper and the lower parts of the eyes 

 is guided at a suitable distance from the vegetation : then a dot of colour, 

 say a buttercup flower, is seen at short range ; at 6 in. it is seen to be 

 lobed, and by a reflex the feet are brought to a position for landing. Satiety, 

 like hibernation, asks for rest ; and the same front facets find a hole which 

 will admit the body — a hole with a contrasting rim is best realised. Colour 

 helps ; for bees see colours, though not quite as we see them. The homing 

 bee apparently sees the landscape in chiaroscuro : and the numbers which 

 fail to home indicate that recognition is difficult. 



Insects' eyes differ enormously in the number of visual units, and prob- 

 ably in receptivity : they are so unlike ours, that it is well to set up an insect 

 type. The best type is the hive bee's. The prodigious diligence of that 

 insect in its simple errand makes it peculiarly useful for experiment. When 

 we pass to insects themselves more brightly coloured, the question of seeing 

 mates and flowers with the same colour-sense comes in. 



Lastly, bilateral symmetry in flowers is in the same plane as bilateral 

 symmetry in a flying insect, and the two are connected. 



Discussion (12.0). 



Dr. C. G. Butler. — Phases in locusts (12.30). 



Uvarov (1921) and Faure (1932) have shown that whereas the species of 

 migratory locusts were formerly regarded as being more or less mono- 

 morphic, they are really polymorphic, and can occur in two extreme forms 

 or phases, i.e. the phase gregaria and the phase solitaria, with a large number 

 of intermediates (phase transiens) between them. 



The phase gregaria differs from the phase solitaria especially in the 

 coloration of the nymphs or hoppers, and in such adult characters as the 

 shape of the pronotum and relative length of other parts of the body. 



Strelnikov (1936) and Butler and Innes (1936) have shown that there are 

 fundamental physiological differences between the phases. 



